The invention relates generally to the detection of ions by ion selective compounds. More particularly, the invention relates to the detection of potassium ions.
Ion selective electrodes are widely used in analytical chemistry to measure the concentration of specific ionic substances in fluids ranging from drinking water to biological fluids, such as whole blood, plasma, serum and urine. Typical ions that have been measured using ion selective electrodes include sodium, calcium, iodide, magnesium, potassium, chloride, and lithium.
Valinomycin is used as an ionophore in the most widely used potassium selective membrane electrodes. 
The antibiotic valinomycin is possibly the best-known neutral carrier for potassium ion in nature. The presence of valinomycin enables the organic membrane to exhibit a voltage (EMF) that is highly dependent on the potassium activity in the sample.
However, there is a need in the art for ionophores suitable for the fluorescent detection of potassium ions.
The invention provides a fluoroionophore based upon the covalent linkage of a fluorophore to a crown-5 calix[4]arene ionophore. The compound (1) has the following general structure: 
where (a) R is hydrogen, a saturated or unsaturated alkyl or aryl group, an ether, a carboxylic acid or ester group, or an alkyl or aryl group containing nitrogen or sulfur, independently or in combination; (b) W is xe2x80x94O(CH2)2O(CH2)2xe2x80x94; (c) X is nitrogen, substituted or unsubstituted aryl, with or without heteroatoms, such as nitrogen, sulfur, oxygen, or saturated and unsaturated alkyl, (d) Y is saturated or unsaturated alkyl or aryl, ether, carboxylic containing, nitrogen or sulfur independently or in combination and (e) Z is an unsubstituted or substituted aryl group or groups (a fluorophore), such that the presence of Z in the compound allows for a negative, thermo-neutral or slightly positive free energy value to be obtained from the Rehm-Weller equation for the compound.
In a particular embodiment, the molecule has the following structure (2): 
where (a) R is propyl; (b) W is xe2x80x94O(CH2)2O(CH2)2xe2x80x94; (c) X is nitrogen, (d)Y is xe2x80x94CH2xe2x80x94 and (e) Z, the fluorophore, is anthracene.
The invention also provides a method of synthesizing the fluoroionophore of the invention. The invention further provides an optode containing the fluoroionophore of the invention.